During my first installation i had the same problem, but when i run mythtv setup, in the capture card menu the card was show as probed info and it worked fine.Don't know if i helped but give it a check.

I did what you suggested there but I've been still having some serious difficulties settings this up.

When I go to the KDE Desktop and select the Myth-TV backend setup it correctly names the device (Hauppauge PVR-150) but it fails to, in some error messages, to open the device. Not only that but from the TV portion of the orbiter menu, when I try to watch the channels directly it tells me that it's failing to connect to the backend. This might be one and the same problem?

I've temporarily disconnected my hybrid from my internal network altogether since it was periodically crashing (I sort of suspected the mythtv backend being the culprit) and planning on reconnecting it as the DHCP server and the whole bit after I had this sorted out. Should it be connected and running as the DHCP server while this is all being set up?

Any help would be greatly appreciated and thank you for your time in advance,

I only run mythtv setup from MCE not KDE desktop, don't know if there's a difference. In pluto admin, if you go to advanced/configuration/devices (top horizontal bar) in the left tree menu you see the card as PVR menu or inside the core/hybrid menu?